[open]

docstring for 'open' function:
------------
Proceed to 'read', 'write', 'append' actions to files

(example)
"filename" "" "r" open => ["This is a content.\n"]
pop "filename" "content" "w" open => []
"filename" "\ncontent2" "a" open => []

Modes combined:
"filename" "This is a new content" "rw" open => ["content\ncontent2"]
pop "filename" "This is a new content" "ra" open => ["This is a new content"]